1. Forces in the Earth – Faults!
Physical Science Notes
10/4/2012

2. Faults
Definition: a fault is a fracture in the Earth where rock movement occurs. This can happen either on the surface or deep beneath the Earth’s surface.
Faults occur at tectonic plate boundaries
Fault 2

3. Faults Fault There are three types of plate boundaries:
Convergent: plates pushed together by compression forces
Divergent: plates pulled apart by tension forces
Transform: plates sliding past each other with shearing forces
Fault 3

4. Faults
Normal Fault
Definition: A normal fault is a fault caused by tension forces at a divergent plate boundary. As a result, rock above the fault moves downward relative to rock below the fault surface. 4

5. Faults
Reverse Fault
Definition: A reverse fault is a fault caused by compression forces at a convergent plate boundary. As a result, rock above the fault moves upward relative to rock below the fault surface. 5

6. Faults Strike-Slip Fault
Definition: A strike-slip fault is a fault caused by shearing forces at a transform plate boundary. 6

7. Faults
Elastic Limit
Definition: Elastic limit measures the farthest something can bend or stretch and still return to its original shape without breaking
Example: Stretching a rubber band. If it snaps, you are past the elastic limit. 7

8. Summarize!
After you summarize, you may begin the homework assignment (summarizing and illustrating each type of plate boundary: convergent, divergent, and transform)

9. Faults
In your notes, please answer the following question in complete sentences:
“How do yesterday’s activities with the Play- Doh, paperclips, and balloons relate to these two terms, fault & elastic limit?”

11. Compression & Transverse Waves
What do you think a compression wave on a spring or slinky would look like? Use your prior knowledge of what compression is (including what you just learned about different forces making faults in the Earth).
Demo!

12. Which wave is faster?
Make a graph comparing the distance from the earthquake focus and the time it took for each kind of wave to travel there.
Set up your graph:
Title: “Compression and Transverse Waves”
X-axis: “Distance from focus (km)” – should go from 250 to 1000 km
Y-axis: “Time of Arrival (hr: min: sec)” – should go from 4 hours to 4 hours: 22 minutes: 45 seconds
Key: which color will stand for compression and which for transverse waves

13. Distance from focus (km) Time of Arrival Hr: Min: Sec COMPRESSION WAVE
Hr: Min: Sec TRANSVERSE WAVE
250
4:01:00
500
4:03:00
1000
4:02:30
1750
4:04:00
2000
4:07:30
3000
4:10:15
4500
4:08:00
5000
4:15:00
6000
4:09:30
7250
4:18:00
8000
4:11:45
8250
4:21:25
9000
4:12:30
9500
4:22:45

14. Conclude & Apply: Answer questions under your graph
Based on your graph, which is faster – a compression wave or a transverse wave?
Do the waves remain the same distance apart as they travel?
Do they grow closer together or farther apart over time?
How could you use your graph to fill in the missing arrival times in the chart?
Use your observations to tell why compression waves are called primary waves and transverse waves are called secondary waves.